1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to a paper feeding mechanism for an image forming apparatus that includes a drive roller and a press roller which are selectively moved apart from each other to prevent unnecessary external forces from being exerted on paper being fed by the mechanism.
2. Description of the Related Art
In general, an image forming apparatus is an apparatus for printing a desired image on paper, such as a printer, a copy-machine, and the like. These apparatuses include a printing mechanism for printing an image on paper and a paper feeding mechanism for feeding paper to the printing mechanism.
FIG. 1 is a perspective view showing one example of a conventional paper feeding mechanism employed in an image forming apparatus. The paper feeding mechanism includes a drive roller shaft 3 rotated by a driving force generated by a driving means (not shown), such as an electric motor. A drive roller 2 is fixed to the drive roller shaft 3, and a press roller 5 is in intimate contact with the drive roller 2 and driven by the drive roller 2. The press roller 5 is pivotably mounted to a hinge shaft 7 at a predetermined angle so that it can be moved away from the drive roller 2, if necessary. The press roller 5 is biased against the drive roller 2 by a spring 8.
The paper feeding mechanism includes a lever 10 pivotally coupled to the hinge shaft 7 so that it is rotatable around the hinge shaft 7 like the press roller 5. A cam 12 presses against the lever 10 to pivot the press roller 5 and move the press roller 5 away from the drive roller 2. An electronic clutch 14 for rotating the cam 12 is provided, if necessary.
When the drive roller 2 of the paper feeding mechanism is rotated, the press roller 5, which is in contact with the drive roller, is also rotated. A leading portion of a piece of paper can be fed into the nip between the rollers 2 and 5 to feed the paper into the printing mechanism. As the leading portion of the paper passes through the printing mechanism, an image is printed on the paper. When the trailing portion of the paper exits from the nip between the rollers 2 and 5, an unnecessary external force is applied to the paper. This unnecessary force reduces the quality of the printed image. Thus, when the trailing portion of the paper exits from the nip between the rollers 2 and 5, the lever 10 is pressed by rotating the cam 12 to move the press roller 5 away from the drive roller 2.
To move the press roller 5 away from the drive roller 2, the conventional paper feeding mechanism illustrated in FIG. 1 requires a complex construction with such parts as the cam 12 and the electronic clutch 14. In addition, the paper feeding mechanism requires means for driving the cam 12, in addition to means for driving the drive roller shaft 3. Therefore, it is difficult to produce a product with a small size and manufacturing costs are increased. Furthermore, the reliability of the paper feeding mechanism is heavily dependent on the performance of the electronic clutch 14. Producing a reliable electronic clutch is very difficult and requires significant costs. Thus, it is difficult to ensure the reliability of the paper feeding mechanism.
Accordingly, there is a need for an image forming apparatus with an improved paper feeding mechanism which is reliable, inexpensive to manufacture, and compact in size.